Vascular plant taxa occurrences in exotic woodland and in natural and production forests on the Islands of São Miguel, Terceira and Pico (Azores)

Abstract Background The data presented here originated from field expeditions carried out between 2017 and 2018, within the framework of Forest-Eco2 project: "Towards an Ecological and Economic valorisation of the Azorean Forest". The project aimed to quantify the ecological value of the Azorean forests, including carbon accumulation and to design and propose measures that could further enhance forest sustainability. For that, 90 forest plots were sampled on three Azores islands - São Miguel, Terceira and Pico - equally distributed into natural forest, exotic woodland and production forest. The aim of this report is to further expand knowledge on biodiversity trends enclosed in the different forest types present in the Azores, by providing a list of the occurrences of the 105 different vascular plant taxa together with a brief characterisation of their origin and life-form. New information We provide an inventory of indigenous and non-indigenous vascular plant taxa from 90 forest stands. A total of 105 taxa were identified and registered, belonging to 60 families, 91 genera, 101 species and four subspecies. A total of 35% of the taxa were endemic, 27% native and 38% non-indigenous, including 19% of invasive taxa. Endangered and vulnerable taxa were registered, including Elaphoglossumhirtum (Sw.) C.Chr., Lactucawatsoniana Trel. and others which were considered by the authors a priority for conservation (e.g. Arceuthobiumazoricum Wiens & Hawksw., Bellisazorica Hochst. ex Seub., Saniculaazorica Guthnick ex Seub., Platantheramicrantha (Hochst. ex Seub.) Schltr.). Our records provide detailed and updated knowledge of Azorean Forest flora and highlight the role of natural forests as indigenous plant diversity hotspots and exotic woodland as a source of invasive taxa within the Archipelago.


Introduction
Studies on ecology and the distribution of organisms in a gradient of forest types, particularly with an emphasis on flora and species attributes, have been the focal point in many projects on forests ecosystems across the world (Rahbek 1995, Kessler 2000, Pavón et al. 2000, Grytnes 2003, Olthoff et al. 2016, Vinod et al. 2022) and also in the Azores Islands , Marcelino et al. 2014, Elias et al. 2016, Borges Silva L et al. 2022b).
Forests and woodlands constitute a striking and structuring element of the Azorean landscape. Occupying about 30% of the insular terrestrial territory (DRRF 2014), they harbour enormous terrestrial biodiversity, making them, in essence, critical habitats for plant species and for providing a wide range of ecosystem services (Matos et al. 2019, Borges Silva L et al. 2022b).
The flora of the Azores comprises about 4000 vascular plant taxa (Tracheobionta) , Borges Silva L et al. 2022a), including cultivated taxa; but excluding another 1397 taxa without a confirmed presence in the Azores. Distributed within several groups, namely Magnoliophyta, Pinophyta, Pteridophyta and Lycopodiophyta , approximately 133 species are considered as native and 101 endemic, distributed over 60 families, the vast majority of which only contain a single endemic taxon , Borges Silva L et al. 2022a). The families with the highest numbers of endemic taxa correspond to Asteraceae (13), Dryopteridaceae (8), Poaceae (12) and Apiaceae (7) (Silva et al. 2009, Moura et al. 2013, Borges Silva et al. 2016, Moura et al. 2018, Moura et al. 2019, Vieira et al. 2020. The remaining taxa consist of exotic plants, distributed over 200 families, 2901 considered as cultivated or at least imported, 322 as casual escapes and 578 as naturalized, of which 140 are invasive, occupying large extensions , Borges Silva L et al. 2022a).
As in many archipelagos, the Azorean primary forest was largely cleared and replaced by secondary forest and grassland (Matos et al. 2019, Pavão et al. 2021. Currently, land use in the Azores is dominated by pastures and agriculture (60%), planted or alien dominated forests (22%), with natural forests and vegetation representing 10% of the territory (DRRF 2014).
This paper aims to publish a dataset of vascular plant occurrences in 90 Azorean forests, highlighting the importance of natural forests as indigenous plant diversity hotspots and of exotic woodland as a source of invasive taxa.

General description
Purpose: The purpose of this paper was to publish a dataset of vascular plant occurrences in three forest types (NF-Natural Forest, EW-Exotic Woodland and PF-Production Forest) on three islands of the Azores Archipelago (São Miguel, Terceira and Pico), already published in GBIF as a Darwin Core Archive.

Project description
Title: Vascular plant taxa occurrences in exotic woodland and in natural and production forests on the islands of São Miguel, Terceira, and Pico (Azores).

Study area description:
The Azores Archipelago is situated in the North Atlantic Ocean, between North America and Europe, about 1500 km west of mainland Portugal, roughly at 38°44'52''N,31°32'16''W and 38°55'27''N,25°0'36''W (Fig. 1). The Archipelago is formed by nine main islands and some small islets, all of them of volcanic origin. The islands are divided into three main groups: the western group (Corvo and Flores), the central group (Faial, Pico, Graciosa, São Jorge and Terceira) and the eastern group (São Miguel and Santa Maria). The climate in the Azores is temperate oceanic, with regular and abundant rainfall, high levels of relative humidity and persistent winds, mainly during winter and autumn (Azevedo et al. 2004).
The landscape of the islands is composed by a mosaic of habitats, ranging from herbaceous to arboreal and from natural to anthropogenic , Soares et al. 2021. The original landscape was strongly altered by replacing pristine and native forest areas with exotic tree plantations, crops, pastures and urban areas . During the last decades of the 20 century, the reduction of native forest area was significant, with the clearing of large fragments, at mid-and high altitude, for pasture ( Gaspar et al. 2008). Pittosporum undulatum, Acacia melanoxylon R.Br. or Eucalyptus th Figure 1.
The Azores Archipelago with its location in the middle Atlantic (right panel) and Azorean Islands namely São Miguel, Terceira and Pico islands (left panel).
globulus dominate most forest patches located in low-to mid-elevation areas. At higher altitudes, Cryptomeria japonica dominates, along with the remaining stands of natural forests, particularly above 600 m a.s.l. (Elias et al. 2016, Borges Silva et al. 2017, Borges Silva et al. 2018, Dutra Silva et al. 2019. The natural vegetation includes diverse communities, namely coastal vegetation, coastal and inland wetlands, meadows, peat bogs and several types of native forests and scrubs. However, forests are the dominant natural vegetation type. In fact, before human settlement, laurel forests could have covered around 75% of Azorean islands (Elias et al. 2016). Currently, the native laurel forest comprises about 5% of the total surface of the Archipelago and has remained only at higher elevations and in inaccessible areas of the islands (Elias et al. 2016).
This research comprised three islands contributing with the largest forest areas: São Miguel Island with 745 km , the highest elevation being 1105 m a.s.l. with an estimated age of 0.79 MY (millions of years) (Sibrant et al. 2015), Terceira Island with 400 km , a maximum elevation of 1023 m a.s.l. and 0.39 MY (Hildenbrand et al. 2014) and Pico Island with an area of 447 km , mostly occupied by a volcanoes reaching an altitude of 2351 m a.s.l. and an approximate age of 0.27 MY (Demand et al. 1982) (Fig. 1).

Design description:
A total of 90 forests patches were randomly sampled, with 30 quadrats plots (100 m , divided into four subplots), per island. Surveys took place in spring and summer of 2017 (São Miguel and Terceira Islands) and 2018 (São Miguel and Pico Islands), for a period of 8 months (4 months per year), corresponding to a total of 240 days. Study areas were delimited using a geographic information system (GIS; QGis 3.28) to map and select forest stands, based on the data provided by the Azorean Forest Inventory (DRRF 2007) (see Borges Silva L et al. (2022b) , Figure 2).

Sampling methods
Description: Three types of vegetation were included (Borges Silva L et al. 2022): • Natural forest, corresponding to submontane and montane cloud forests (Elias et al. 2016). Its distribution in the Azores evolved in unique conditions, due to a pronounced isolation, relatively homogeneous climatic conditions and a limited number of native woody species, but high plant biodiversity and a high number of endemic species, which are dominated by Ilex azorica Gand., Juniperus brevifolia (Hochst. ex Seub.) Antoine, Laurus azorica (Seub.) Franco, Morella faya (Aiton) 2 2 2 2 Vascular plant taxa occurrences in exotic woodland and in natural and production ...

Wilbur and
Picconia azorica (Tutin) Knobl (Dias et al. 2007, Elias and Dias 2008, Pavão et al. 2023a, Pavão et al. 2023b). • Exotic woodland, located at lower to mid-elevations and dominated by P. undulatum covering more than 30% of the forest area, which expanded from sea level up to 600 m (Borges Silva et al. 2017, Dutra Silva L et al. 2017a, Dutra Silva et al. 2017b, Borges Silva et al. 2018, Dutra Silva et al. 2019). • Production forest, dominated by C. japonica, occupying 60% of the area dedicated to this type of forest, the most economically important forestry species in the Azores and with an important impact on the landscape (DRRF 2007, Lourenço et al. 2011, DRRF 2014. Sampling description: A total of 90 forest stands were randomly sampled, 30 in each of the three selected islands São Miguel, Terceira and Pico (10 NF, 10 EW and 10 PF) ( Table  1). At each forest, we delimited a 10 × 10 m (100 m ) plot and recorded the vascular plant taxa. To quantify the cover-abundance of each taxon, we used the Braun Blanquet scale modified by Van der Maarel E (1979).

Analysis
Colonisation status. We determined the indigenous and non-indigenous plants globally and specifically for the groups Magnoliopsida, Liliopsida, Pinophyta, Pteridophyta and Lycopodiophyta. The contribution of each family was evaluated by calculating the number of genera for indigenous and non-indigenous taxa within each family and the number of infrageneric taxa per genus.

Biogeography of non-indigenous plants.
The distribution of non-indigenous taxa was classified by region, according to Pielou (1992). Taxa present in more than two biogeographic regions were considered as subcosmopolitan.
Useful species. The number of taxa in the following categories was calculated: ornamental, forestry, cultivated (aromatic, animal fodder, hedge-plants), crops (human food) and ruderal. The percentages of taxa considered as plant invaders and as ecological threats by Portuguese legislation were also calculated DLR 15 from 2 April 2012 (DLR15 2012) and DL 92 from 10 July 2019 (DL92 2019).
Quality control: Specimens representing most of the inventoried species, were collected in the field, following standard herbarium techniques and then deposited in the Herbarium Ruy Telles Palhinha, University of the Azores (AZB). All sampled individuals were sorted by trained taxonomists.
Taxonomic nomenclature obtained from:Seubert and Hochstetter (1843) In terms of species colonisation status, we followed Silva et al. (2010) categories: Azorean endemic species, i.e. species (or subspecies) occurring only in the Azores, as a result of either speciation events (neo-endemics) or extinct of the mainland populations (paleoendemics); Macaronesian endemic species, i.e. species only known from the Macaronesian archipelagos (the Azores, Madeira, Canaries and Cape Verde); Native species, i.e. species which arrived by long-distance dispersal to the Azores and which also occur naturally elsewhere. Regarding Introduced species, that occur in the archipelago as a result of human activities, we distinguished two groups, Naturalised, with self-supporting populations and Casual, occasionally escaped from cultivation.
The biogeographic and historic criteria used to classify taxa as non-indigenous were adapted from : (i) classified as such by several authors from the 19 century; (ii) first record in the last 100 years; (iii) distribution restricted to a reduced number of islands; (iv) record of a recent (last 100 years) extension of the distribution in the Azores; th (v) absence in other Macaronesian islands; (vi) disjunct distribution; (vii) anthropochoric taxa -only casual in the native vegetation. These criteria were applied after exclusion of endemic taxa. Database queries allowed the determination of the taxa number in each category, globally and specifically for the Magnoliopsida, Liliopsida, Pinophyta, Pteridophyta and Lycopodiophyta groups (Silva and Smith 2004 2 and Fig. 3). Magnoliopsida were the highest proportion and Pinophyta the lowest (Fig. 2  and Fig. 3). The 105 taxa were distributed by 60 families belonging to 91 genera (Fig. 2). In general, each family and genus contributed only with a small number of indigenous (1-6) or non-indigenous taxa (1-3) (Fig. 2).
Regarding Magnoliopsida, NF showed the highest numbers of endemic and native taxa, while EW and PF showed the highest values of invasive taxa, EW also showing a high number of naturalised and casual species (Fig. 2). For Liliopsida, again NF showed the highest values of endemism, despite also including naturalised and invasive taxa (Fig. 2). For Pteridophyta, all three forests showed similar values of endemic, native and invasive taxa (Fig. 2).
In the Pteridophyta, for the three forest types, 10 families included one or two genera, one family included three genera and only two families participated with more than two species, namely the Dryopteridaceae and Hymenophyllaceae (Table 2). We found two Lycophytes, one a Macaronesian endemism, Huperzia suberecta (Lowe) Tardieu. The Pinophyta only included two Cupressaceae, with one endemic taxon, Juniperus brevifolia (Hochst. ex Seub.) Antoine subsp. brevifolia (Table 2). For the three forest types, the Liliopsida included 11 families and 27 genera, most contributing with only one taxon. The Cyperaceae and Poaceae included the highest numbers of indigenous taxa (Table 2). For the Magnoliopsida, we found 35 families and 83 genera. In general, the families including more indigenous taxa were the Asteraceae, Ericaceae, Lauraceae and Rosaceae (Table  2).    The frequency of indigenous vascular plant taxa showed the highest values for NF (55% endemic and 38% native) and the lowest for EW (23% endemic and 25% native) and PF (17% endemic and 18% native) (  Table 3. ; T100 (100 priority threatened species for management in the European biogeographical region of Macaronesia); CITES; R4 (protected by regional interest); P (priority for conservation) and *(priority European species).
Woodwardia radicans (L.) Sm. NAT X X X X X X X X VU Regarding the conservation status of indigenous vascular plant taxa, we found 23 considered as Least Concern (LC) and two as Endangered (EN) in NF and in the three forest types, two as Vulnerable (VU) and two as Near Threatened (NT) ( Table 3). We also found particularly rare species such as Lactuca watsoniana Trel. In total, 36 indigenous species (55%) had not been evaluated by IUCN criteria (Table 3).
Although, based on DLR no. 15/2012/A (DLR15 2012), 35% of the indigenous species in the current study are covered by measures for conservation and protection (Table 3), of these 60% are proprietary for conversion (P) and all taxa present in NF, 13% EW and 9% PF (Table 3).

Life forms
The majority of indigenous and non-indigenous Pteridophyta were hemicryptophytes, 60% and 75%, respectively, while Pinophyta only included one megaphanerophyte and one microphanerophyte.
Non-indigenous and indigenous Magnoliopsida included a larger proportion of phanerophytes than Liliopsida (Fig. 4), while geophytes and hemicryptophytes were of some importance in the Liliopsida (Fig. 4).

Biogeography of non-indigenous plants
Most non-indigenous taxa had a wide geographic distribution. About 75% were Subcosmopolitan and a considerable percentage had a Palaearctic distribution (Fig. 5).

Useful species
Almost all non-indigenous Pteridophyta were ornamental plants, while the Pinophyta were forest species (Fig. 6). The Magnoliopsida included a large proportion of ornamental and ruderal plants. The Liliopsida included a large percentage of ornamental and a small proportion of ruderal taxa (Fig. 6).    Percentage of non-indigenous vascular plants (naturalised or casual) with human utilisation (ornamental, forest species and food crops) or ruderal, for the three forest types in São Miguel, Terceira and Pico Islands, Azores. The data labels correspond to the number of taxa.

Data format version: Version 1.2
Description: The dataset was published in Global Biodiversity Information Facility platform, GBIF (Borges Silva et al. 2023).The following data table includes all the records for which a taxonomic identification of the species was possible. The dataset submitted to GBIF is structured as a sample event dataset that has been published as a Darwin Core Archive (DwCA), which is a standardised format for sharing biodiversity data as a set of one or more data tables. The core data file contains 90 records (eventID). This IPT (integrated publishing toolkit) archives the data and thus serves as the data repository. The data and resource metadata are availabe for download from Borges Silva et al. (2023).  (Borges Silva et al. 2023). The following data table includes all the records for which a taxonomic identification of the species was possible. The dataset submitted to GBIF is structured as a occurrence table that has been published as a Darwin Core Archive (DwCA), which is a standardised format for sharing biodiversity data as a set of one or more data tables. The core data file contains 1150 records (occurrenceID). This IPT (integrated publishing toolkit) archives the data and thus serves as the data repository. The data and resource metadata are available for download from Borges Silva et al. (2023). The frequency of indigenous vascular plant taxa was highest for NF (55% endemic and 38% native) and lowest for EW (23% endemic and 25% native) and PF (17% endemic and 18% native). Pico Island displayed the highest number of indigenous species in NF and the lowest number in PF. The results of this study agree with data from previous investigations (Borges Silva L et al. 2022b). As expected, natural forests correspond to indigenous plant diversity hotspots and exotic woodland works as a source of invasive taxa.

Column label Column description
According to our results, 35% of the indigenous plant taxa in the current study are covered by conservation regulations.
The list of the vascular plants found in our study devoted to natural and production forests and to exotic woodland in three Azores Islands, clarifies the type of flora to be expected in the forested areas in the Azores, emphasising the relevant role of the former as hotspots of native biodiversity, which agrees with previous studies for the Azores , Mendonça 2013, Marcelino et al. 2014, Elias et al. 2016, Borges Silva et al. 2018, Borges Silva L et al. 2022b.
As stated by Borges Silva L et al. (2022b), natural forests mainly corresponded to montane forests which occur in the thermotemperate-hyperhumid and ultrahyperhumid belts, from 600 to 1000 m a.s.l., in areas with high rainfall (3000 to 5000 mm year ) and occult precipitation (cloud forests) Bates 2005, Elias et al. 2016). These forests have small stature and are frequently subjected to natural disturbances (Elias et al. 2011). This favours plant diversity by allowing the existence of both light-demanding and shade −1 tolerant species. They are characterised by a high percentage of endemic species, trees covered by epiphytes and a complex vertical structure with several layers (Elias et al. 2016).
Meanwhile, the role of exotic woodland and, to a lesser extent, of production forest, as reservoirs of invasive species is also confirmed (Borges Silva L et al. 2022b). The low plant diversity noted in EW and PF could be explained by the dominance of a single species (Pittospotum undulatum and Cryptomeria japonica, respectively), contributing with nearly 90% of the total number of trees per plot and dominating the canopy where only ferns and a few invasive species that tolerate low levels of light intensities below 1% full sunlight at ground level (e.g. Hedychium gardnerianum) are found (Gleadow and Ashton 1981, Gleadow et al. 1983, Cordeiro and Silva 2003, Borges Silva L et al. 2022b).
Regarding anthropogenic action, NF have less human influence and are hard to access (Ramos 1996). Disturbances are limited to minor harvesting of non-timber forest products (Borges Silva L et al. 2022b). Nevertheless, active and persistent conservation measures are needed to ensure the preservation of the natural forests in the Azores. In the case of PF and the spread of invasive species in EW, an intensive management regime resulted in a decrease in plant diversity levels , Castro et al. 2010, Kueffer et al. 2010, DRRF 2017. While plantations are known for high timber productivity, their potential to harbour plant diversity is low (Borges et al. 2019). In the Azores, the new production forests already include a buffer zone with native elements (DRRF 2017). However, management plans should be developed for exotic woodland, following the guidelines already established for the renovation of Cryptomeria japonica production forests in the Azores.
Finally, we consider that our dataset and the derived conclusions will be useful for future conservation and research activities, as well as for forest managers, in the development of more comprehensive action plans, particularly on islands.

Author contributions
LBS with conceptualisation and writing original draft, carried out field and lab work, data collection and analysis, writing-review and editing. LS conceived the project, carried out fieldwork, data collection, writing-review and editing. DP carried out field, lab work, data collection. RBE carried out field, lab work, data collection, review. MM carried out fieldwork, data collection. PM review. All authors have read and agreed to the published version of the manuscript.